PROOF-TREE

A view of ACL2 proofs may be obtained by way of ``proof tree
displays.'' The emacs environment is easily customized to provide
window-based proof tree displays that assist in traversing and
making sense of the proof transcript; see proof-tree-emacs.
Proof tree displays may be turned on with the command :start-proof-tree
and may be turned off with the command :stop-proof-tree;
see start-proof-tree and see stop-proof-tree.

See proof-tree-examples for many examples that contain proof
tree displays. But first, we summarize the kinds of lines that may
appear in a proof tree display. The simplest form of a proof tree
display is a header showing the current event, followed by list of
lines, each having one of the following forms.

n <goal> <process> ...

Says that the indicated goal created n subgoals using the
indicated process. Here ``...'' refers to possible additional
information.

c n <goal> <process> ...

As above, but calls attention to the fact that this goal is a
``checkpoint'' in the sense that it may be of particular interest.
Some displays may overwrite ``c'' with ``>'' to indicate the current
checkpoint being shown in the proof transcript.

| <goal> ...
| | <k subgoals>

Indicates that the goal just above this line, which is pointed to
by the rightmost vertical bar (``|''), has k subgoals, none of which
have yet been processed.

| <goal> ...
| | <k more subgoals>

As above, except that some subgoals have already been processed.

++++++++++++++++++++++++++++++

Separates successive passes through the ``waterfall''. Thus, this
``fencepost'' mark indicates the start of a new proof by induction
or of a new forcing round.